Dispersion patterns of carbonyl sulphide above mineral deposits

Abstract

Thermodynamic calculations and experiments in vitro have pointed to the potential value of carbonyl sulphide (COS) as a gaseous pathfinder for sulphide mineral deposits concealed beneath overburden. Convenient sampling and analytical techniques have, therefore, been developed for the determination of COS in overburden materials. In temperate regions, samples of soil are taken below the normal rooting depth of vegetation; in arid and semi-arid regions the surface microlayer is collected. The analytical procedure involves the selective thermal desorption of COS from the < 150 μm fraction of overburden materials and quantitative determination by a rapid gas chromatographic method. Field studies of surficial dispersion patterns of COS have been carried out in the vicinity of replacement-type Cu (-Zn) and porphyry Cu deposits in the southwestern U.S.A., meta-sedimentary Cu-Zn mineralization in Saudi Arabia, volcano-sedimentary polymetallic sulphides in South Africa and stratabound Pb-Zn mineralization in Ireland, and are described here. These deposits are covered by different types and various thicknesses of overburden material. Anomalous concentrations of COS occur in the overburden above all of these deposits. The anomalies tend to be of modest but satisfactory contrast and are in some instances discontinuous or patchy. Results indicate that COS may be used as a guide to concealed mineral deposits in a variety of geologic and physiographic settings. Significant anomalies can be recognized even where mineralization lies beneath more than 90 m of transported overburden.